The present invention relates to the field of electronic circuit technology; in particular it relates to a low-voltage to high-voltage level shifter circuit.
To achieve high performance and high integration density, transistor dimensions are aggressively scaled down in the ultra-deep submicron process and nanometer process, while low power dissipation is achieved by scaling down the supply voltage even under 0.7 V or 0.9V. In various electronic devices, integrated circuits operating at low supply voltages are interfaced with electronic circuits operating at higher supply voltages. For example, a chip set operating at a first core voltage level (VDDL) can interface with a memory device operating at a higher voltage level (VDDH), for example, at 1.4 V. In addition, many kinds of I/O voltages such as 1.5V, 1.8V, 2.5V and 3.3V are needed in the I/O interface part.
A conventional voltage converter circuit is often used as a bridge for connecting low-voltage circuits and high-voltage circuits. For example, a voltage shifter circuit can be used to connect a low-voltage core logic to a high-voltage I/O interface circuit to obtain a higher drive current.
FIG. 1 is a circuit diagram of a conventional voltage shifter circuit. As shown in FIG. 1, the voltage converter circuit includes transistors M101, M102, M103, M104, M105, and M106, in which transistors M101 and M102 may be thin gate oxide transistors, and transistor M103 and M104 may be thick gate oxide transistors.
As shown in FIG. 1, the current driving capability of transistors M105 and M106 are affected by the threshold voltage of each transistors, and they are not affected by the high-voltage power supply VDDH. In this way, a stable current driving capability can be maintained, suitable for a wide range of high-voltage power supply VDDH.
However, the inventor has observed that, in FIG. 1, when input IN is high, transistors M103 and M105 are open simultaneously, thus forming a path from the power supply to ground leakage current path. Since the transistors M103 and M104 are thick gate-oxide transistors having high threshold voltages, a conventional low-voltage to high-voltage shifter circuit, such as the one shown in FIG. 1, cannot be applied to ultra-low input signal voltages.
FIG. 2 is a circuit diagram of another conventional low-voltage to high-voltage shifter circuit. As shown in FIG. 2, the voltage converter circuit includes transistors M201, M202, M203, M204, M205, and M206, in which transistors M201 and M202 are thin gate oxide transistors, and transistors M203 to M206 are thick gate oxide transistors. In the low-voltage to high-voltage shifter circuit in FIG. 2, thick gate-oxide PMOS transistors M207 and M208, along with thick gate oxide NMOS transistors M203 and M204, form an inverter and can quickly cut off the leakage current from the power supply to ground to improve the operating frequency.
However, the inventor has observed that the addition of thick gate-oxide MOS transistors M207 and M208 increases the minimum required power supply voltage VDDH. As a result, the low-voltage to high-voltage shifter circuit shown in FIG. 2 is not suited for wide output voltage applications.
In the meanwhile, with the enhancement of system performance, high speed becomes increasingly important. The inventor has also observed that conventional level shifter circuits often fail to meet the high speed requirements.
Therefore, an improved design of the low-voltage to high-voltage shifter circuit is highly desirable.